From the published patent DE 103 05 241 A1, a six or seven-geared double clutch transmission is known. The double clutch transmission comprises two clutches, each of which has an input side connected to the drive shaft and an output side connected to one of the two transmission input shafts. The two transmission input shafts are arranged coaxially to each other. In addition, two countershafts are arranged parallel to the axis of the two transmission input shafts which have idler gears meshed with fixed gears of the transmission input shafts. Furthermore, coupling devices are held in a rotationally fixed manner and axially adjustable on the countershafts in order to be able to shift each toothed gearwheel. Each selected transmission ratio is transmitted over the power take-off gears to a differential. To achieve the desired transmission ratio steps with the known double clutch transmission, a multiplicity of gear planes are necessary, which results in the need for a not insignificant construction space during assembly.
Furthermore, a spur-gear multi-speed transmission is known from published patent DE 38 22 330 A1. The spur-gear multi-speed transmission comprises a double clutch which can be power-shifted, of which one part is connected to a drive shaft and another part is connected to a hollow drive shaft that is rotatably fixed on the drive shaft. For certain transmission ratios, the drive shaft can be coupled with the hollow drive shaft via a shift element.
From published patent DE 10 2004 001 961 A1, a power-shift transmission with two clutches is known, each assigned to a subtransmission. The transmission input shafts of the two subtransmissions are arranged coaxially to each other and mesh, via fixed gears, with idler gears of the assigned countershafts. Each of the idler gears of the countershafts can be connected to each countershaft by the assigned shift elements in a rotationally fixed manner. This published patent makes known, among other things, a seven-geared transmission, in which an additional shift element for coupling the two transmission input shafts is provided for the realization of a further transmission ratio step. The seven-geared transmission requires at least six gear planes in both subtransmissions in this embodiment to attain the transmission ratio steps. This leads to an undesirable lengthening of the construction length in the axial direction, limiting the possibility of mounting into a vehicle.
Furthermore, published patent DE 10 2005 028 532 A1 makes known an additional power-shift transmission, which comprises two input shafts and only one countershaft. The seven-geared transmission requires at least five gear planes in this embodiment to be able to realize the transmission ratio steps, which leads to an undesirable lengthening of the construction length in the axial direction. Moreover, an additional shaft with one gear plane is necessary, which comprises one shift element and two gears for the attainment of the reverse motion transmission ratios. Another disadvantage of the known power-shift transmission is that power-shifting is only possible between the first and second gears.